1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an automatic document feeding (ADF) device feeding documents that are stacked one by one to a scanning unit scanning images recorded on the documents and an image forming apparatus including the ADF device.
2. Description of the Related Art
Generally, an image forming apparatus receives an image signal and transfers the image signal onto a sheet of paper to form a visible image. In particular, an image forming apparatus having a scanning function, such as a facsimile or a scanner, scans an image recorded on a document, converts the image into digital image information, which may be reproduced on a sheet of paper or a display. The image forming apparatus with the scanning function includes a scanning unit scanning an image on a document and an automatic document feeding (ADF) device feeding each page of the document to the scanning unit (the so-called “automatic document feeding” function).
FIG. 1 is a sectional view of a conventional ADF device. Referring to FIG. 1, the conventional ADF device includes an ADF roller 3 rotating above a document feed tray 20 and feeding documents D, and a pickup roller 8. The ADF roller 3 is coupled to an ADF roller shaft 5 powered and rotated by a driving unit (not shown), and the ADF roller shaft 5 penetrates a bracket 1. The pickup roller 8 is rotatably coupled to a pickup roller shaft 9 supported by the bracket 1.
A document stopper 10 forcing front ends of the documents D to be disposed under the pickup roller 8 is coupled to the pickup roller shaft 9. A lower end of the document stopper 10 is disposed in a slit 21 formed in the document feed tray 20, and an upper end of the document stopper 10 is caught on and locked in a hook 13 of a latch arm 12. Thus, the document stopper 10 is prevented from rotating. The latch arm 12 is rotatably coupled to a cover 15. Meanwhile, reference numeral 14 indicates a center of rotation of the latch arm 12, and an ADF pad 4 is attached to the ADF roller 3.
To be scanned, the documents D are stacked on the document feed tray 20. The front ends of the documents D are blocked by the document stopper 10, and the documents are arranged under the pickup roller 8. When a scan command is input to an image forming apparatus, the ADF roller shaft 5 rotates in a counter-clockwise direction, and so does the bracket 1. Accordingly, the pickup roller 8 descends and contacts a front end of an uppermost document D of the documents D stacked on the document feed tray 20. As the pickup roller 8 descends, the upper end of the document stopper 10 coupled to the pickup roller shaft 9 breaks away from the hook 13 of the latch arm 12 to become unlocked, and thus rotatable.
Then, the pickup roller 8 rotating in the counter-clockwise direction picks up one through several documents D and transports the one through several documents D to the ADF roller 3. The ADF roller 3 rotating in the counter-clockwise direction feeds the uppermost document D of the transported one through several documents D to a scanning unit (not shown).
When a plurality of documents D are stacked on the document feed tray 20, a weight of the documents D acts on a lower portion of the document stopper 10, thus creating tremendous friction between the hook 13 of the latch arm 12 and the upper end of the document stopper 10 that are in contact with each other.
Due to this friction, although the ADF roller shaft 5 rotates in the counter-clockwise direction in response to the scan command input to the image forming apparatus, the bracket 1 cannot rotate. Consequently, the pickup roller 8 fails to pick up the documents D, thus jamming the documents D or stalling a motor.
To solve this problem, it has been suggested that a separate motor in addition to the motor connected to the ADF roller shaft 5 be installed to rotate the bracket 1. However, this addition complicates the configuration of the ADF device, thus increasing manufacturing costs, and requires greater power consumption to drive the separate motor.